In the manufacture of armatures and commutators, a number of operations must be performed on the commutator. For example, each commutator bar must have a slot formed therein for receiving the armature wires. After the slots have been formed in the commutator bars, the armature wires are inserted therein, and then a fusing or brazing operation is performed to weld the armature wires in place. Also, an undercutting operation is typically performed on the commutator to cut out the insulating mica between the commutator bars so that it does not wear out the contacting brushes. In order to perform each of these operations, it is necessary to mount the armature and commutator for rotation so that successive commutator bars can be indexed into operating position. In addition, in order to automate such operations, it is necessary for the machine performing the operations to know whether a commutator bar is in the proper position to be operated on. For example, in order to form a slot in each commutator bar, it is necessary for the commutator to be rotated to bring the central area of each commutator bar into proper position, and then the rotation is stopped and a cutting tool is actuated to form the slot in the commutator bar. The commutator is then rotated to bring the next commutator bar into position so that a slot can be formed therein.
In the prior art, a number of ways have been developed to bring each successive commutator bar into operating position. For example, in one prior art arrangement, a ratchet and indexing mechanism are employed, with the ratchet having the same number of teeth as the commutator has bars. In this manner, each operation of the ratchet brings the next commutator bar into position. Such an arrangement has been generally satisfactory, where the commutator has a relatively small number of commutator bars, such as twenty-five. However, in those cases where the commutator has, for example, one hundred or more commutator bars, such an arrangement has proven to be unsatisfactory. In such cases, with such a large number of commutator bars, the bars are difficult to manufacture with great accuracy, so that some commutator bars may be of slightly different widths, and the spacing between commutator bars may also vary slightly. As a result, as the commutator is rotated to bring each of the one hundred bars into operating position, the inaccuracies accumulate such that, in many instances, the operation to be performed on the commutator bar is not performed at the right location. For example, a slot may be formed in the commutator bar, such that it overlaps the insulating mica between adjacent commutator bars. As a result, the entire commutator is defective.
In another prior art arrangement, a light source is employed to direct a light beam to the surface of the commutator, and a photocell is employed to detect the reflection of light from reflective areas of the commutator surface, or the non-reflection of light from non-reflective areas of the commutator surface. Such light sensing devices are then employed to actuate a tool for performing an operation on the commutator, such as the slotting tool for forming a slot in the commutator bar, or the stuffing tool for inserting armature wires into the commutator slot, or a fusing or brazing tool. However, the drawback with such an arrangement is that there has been a problem with ambient and/or stray light being detected by the light sensor which causes a tool to be actuated and to perform an operation on the commutator at an incorrect location which causes a defect in the commutator.
Another prior art arrangement is disclosed in U.S. Pat. No. 3,911,563 which recognizes that there are inaccuracies in the manufacture of commutators, such that the spacing between commutator bars is not uniform, and also that there are inaccuracies with respect to the spacing between slots that are cut into the commutator bars. This prior art patent accepts such inaccuracies and attempts to correct for them by controlling the drive means which rotates the commutator. To accomplish this, sensing apparatus is provided to identify the actual characteristics of the commutator, which are recorded in the memory of a computer to be used in effecting accurate indexing of the commutator. Accordingly, in such an arrangement, the commutator must be rotated through two complete revolutions: one revolution is for the computer to be supplied the actual characteristics of the commutator, and the second revolution is for performing a work operation on the commutator. Such a system is time consuming and requires complex and costly apparatus. In addition, even such a complex and costly system is also subject to the drawback discussed above of the light-sensing device being subject to ambient and/or stray light which causes inaccuracies in the system.
Accordingly, it is an object of the present invention to provide an improved apparatus which overcomes the aforesaid problems. Specifically, it is within the contemplation of the present invention to provide an improved apparatus which is simple and inexpensive, yet avoids the problems that the prior art arrangements have experienced with respect to ambient and/or stray light.
It is a further object of the present invention to provide an improved apparatus for accurately sensing predetermined locations on commutators which are inaccurately manufactured and, in response thereto, actuating tools for performing manufacturing operations on the commutator, such as slotting, stuffing of armature wires, fusing, or undercutting.